The present invention relates to the structure of a chord truss roof which is adapted to be stressed in a predetermined manner by tensioning its cable or chord members to support itself with no strut provided in the center.
As one of the construction types of long span structure roofs, there is a chord truss roof structure.
A roof of the conventional chord truss roof has an annular ring-girder figures. The ring girder is composed of a compression ring and a tension ring which are respectively located at upper and lower positions in the ring-girder and joined to each other by struts. Installed on the compression ring is a roof light window. Cross beams are radially arranged around the ring-girder and respectively joined to the outer periphery thereof. Plural beams and braces are provided between and joined to adjacent cross beams to form a trussed roof. Furthermore, cable or chord members are stretched between outer ends of the respective cross beams and the tension ring at the bottom of the ring-girder. The chord members are tensioned to stress the roof structure. More particularly, the tensions acting on the respective chord members cause forces for pushing up the crossbeams 4; cross beams; the forces are transmitted through the struts to the cross beams, so that the roof can support itself. Side wall sections are separately constructed, and the roof is laid on the side wall sections with its outer ends supported by upper end portions of the side wall sections. Incidentally, seat portions are provided inside the side wall sections.
The building having the roof 8 of this structure is constructed, for instance, in the procedure shown in FIGS. 7 to 9.
First of all, as shown in FIG. 7, steel frames of the side wall sections 5 of the building are erected with cranes, and a working platform 11 for the ring-girder is assembled in approximately the center of the building. Then, the ring-girder 1 is assembled with the support by the working platform 11 as shown in FIG. 8. The ring-girder 1 is, for instance, of a circular shape as viewed from above, and the tension ring 3 is formed at the bottom of the ring-girder.
Subsequently, a skeleton or structural body work is executed on the steel frames with reinforced concrete. The cross beams 4 are laid one after another with the cranes between the upper end portions of the side wall sections 5 and the ring-girder to be assembled in an arcuate shape as viewed from the side and in a circular shape as viewed from above. The beams, braces and so forth are installed to form the chord truss roof.
After the above work, the chord members 6 are installed between the respective outer ends 4a of the cross beams 4 and the tension ring 3 at the bottom of the ring-girder 1, as shown in FIG. 9. Subsequently, the chord members 6 are tensioned to exert a required stress on the trussed roof thus assembled, so that the trussed roof can support itself. The chord truss roof 8 is thus completed, and the working platform 11 is removed.
In addition, after the tensioning, roofing materials, etc. are installed by adhesion over the chord truss roof 8, and finish works, such as a waterproofing work and so on, are performed to complete the whole work.
However, in the chord truss roof 8 of the above structure, the chord members 6 on both sides of the ring-girder 1 are continuous so that each extends across the ring-girder 1 from the outer end 4a of one cross beam 4 to the outer end 4a of an opposite cross beam 4. In the case of the chord truss roof 8 of a large size therefore, each chord member 6 also becomes long accordingly and when tensioning the chord member 6, a jack which is a means for tensioning has to have a sufficiently long stroke. For this reason, it is necessary when tensioning the chord members 6 to provide jacks of large sizes. Improvement of the structure in this respect has been desired. Additionally, since the tension ring 3 at the bottom of the ring-girder 1 is subjected to forces for inwardly thrusting the same due to the tensioning of the chord members 6, the tension ring 3 needs reinforcing.